1. Field of the Invention
The present invention relates to a printing apparatus and aging method and, particularly, to an inkjet printing apparatus which prints by discharging ink droplets to a printing medium, and an aging method therefor.
2. Description of the Related Art
Recently, inkjet printing of discharging ink from orifices to form and print an image or the like on printing paper has been widely adopted as a printing method for printing apparatuses because it is non-impact printing and is capable of low-noise, high-density, and high-speed printing. A printing apparatus of this type includes a mechanism which drives a carriage supporting an inkjet printhead (to be referred to as a printhead hereinafter), a conveyance mechanism which conveys a printing medium such as printing paper, and a control unit which controls them.
The following methods have been conventionally known as a method of generating energy for discharging ink from the orifice of a printhead: a method of pressurizing ink by using an electromechanical transducer such as a piezoelectric element; a method of using the pressure of a bubble generated by heat generated by irradiation of an electromagnetic wave such as a laser beam; and a method of heating and bubbling ink by an electrothermal transducer (to be referred to as a heater hereinafter).
In a printhead using an energy generation method using a heater, when ink is heated by the heater and burned on the surface of the heater, the ink discharge velocity relatively greatly changes in some cases. The coloring agent of the ink used in this printhead is often a dye or pigment. These coloring agents are insoluble or hardly-soluble in water, and thus the ink is considered to be burned on the heater.
The burn causes several problems. For example, if the discharge velocity changes owing to burn, the landing position of ink discharged in the forward direction and that of ink discharged in the backward direction shift from each other in printing by reciprocal scanning of the printhead (to be referred to as a registration error in the reciprocal direction hereinafter). This impairs the reproducibility of a fine portion of an image or a thin line (especially a vertical ruled line), resulting in poor image quality.
An attempt has been made to perform preliminary discharge (to be referred to as aging hereinafter) not contributing to printing on a printing medium by a printhead, accelerate the burn of ink attached to the heater surface to some degree, and uniform the burn on the heater surface so as to stabilize ink discharge. In aging, a target orifice performs the same ink discharge operation as normal ink discharge. However, for example, a pulse of a voltage value larger than a voltage pulse normally applied in printing is applied to the electrothermal transducer, or a pulse is applied for a time longer than the time of a normally applied pulse. This ink discharge operation can uniform the burn on the heater surface and stabilize ink discharge.
In the aging operation, ink is discharged into a dedicated ink receptor or cap, similar to the preliminary discharge operation in recovery processing. Aging processing is sometimes started in accordance with, for example, an instruction input by the user or an automatic sequence when a printing apparatus is used for the first time after purchase or when a detachable printhead is mounted.
The above-described conventional technique is disclosed in, for example, Japanese Patent Laid-Open No. 2004-262066.
However, when the user uses a printing apparatus for the first time after purchase or when a detachable printhead is mounted, if aging processing is performed for all nozzles, a large amount of ink is wasted. In addition, the number of media printable with ink contained in an ink tank at the beginning of use decreases disadvantageously.
Further, if aging is performed for all nozzles, the temperature of the printhead rises and abnormal discharge occurs. To avoid this, the printing apparatus needs to stand by until the temperature of the printhead becomes equal to or lower than a predetermined value during aging. As a result, aging processing takes a long time. These problems are becoming more serious than in the conventional printing apparatus because of a large number of nozzles (long printing length) integrated in a printhead for recent high-speed printing.